Overweight and obesity are growing problems; for example over 60% of the American population can be classified as overweight or obese. Weight gain occurs when a human has a higher energy intake (food) than energy expenditure (resting metabolic rate+activity). Since this unbalance causes the weight gain problem, many weight loss programs require that users log the food consumed and activities done in order to estimate the calorie balance.
Tables and equations exist for converting nutrition values and activities into calorie intake and expenditure, respectively. However, manual calorie counting is a cumbersome process requiring knowledge, time, effort, recording and discipline. Thus, calorie logging is a problem for many people and hence it is a challenge for researchers to find a solution therefore.
In US patent application publication US2003/0065257, a combination of a diet and activity-monitoring device is described for monitoring both the consumption and activity of the subject. Such a monitoring device includes a body activity monitor for monitoring the body activity of the subject. The body activity monitor is operable to output a signal indicative of the subject's body activity. An activity calculator may also be provided, which receives the activity indicative signal and determines body activity level and/or energy expenditure for the subject. The monitoring device may take the form of a wristwatch-style device or a belt or clothing-mounted monitor. The monitoring device may comprise a heart rate monitor. The heart rate of the subject increases with activity and decreases when the subject is resting. The activity monitor may be calibrated using an indirect calorimeter. The heart rate sensor may be part of the wristwatch-style activity monitor, or it may be provided as a separate unit, for example in the form of a chest-strap, which communicates with the activity monitor.
The activity monitor may alternatively comprise a motion sensor such as a mechanical pendulum or a single or multi-axis accelerometer. An accelerometer is preferred since it may provide information on body movement as well as the direction and intensity of the movement. The motion sensor may form part of the wristwatch or belt or clothing-mounted monitoring device or may be part of a separate accessory that communicates with the monitoring device. The body activity monitor may be calibrated to determine activity-related energy expenditure using an indirect calorimeter.
As another alternative, the body activity monitor may include multiple modes for recording a variety of activities, such as swimming, biking, and use of stationary exercise equipment. The subject presses a start button and the body activity monitor will record the duration of the activity.
Furthermore, the monitoring device also preferably includes a consumption notation control for use by the subject to indicate when the subject consumes food. The body activity monitor and the consumption notation control may take a variety of forms. It may include a GPS antenna to determine the position of the subject using GPS signals. It may combine a time-indicative signal with the GPS signals to determine changes in position of the subject as well as the rate of change in position. This allows determination of movement or body activity. The device may be calibrated to determine caloric expenditure from the measured body activity.
Moreover, a position and/or activity discriminator may be included in or communicating with the body activity monitor. The discriminator functions to determine the position and/or activity of the subject by determining the proximity of the subject to various devices and locations, such as exercise equipment and buildings. For example, it may be determined that the subject is close to running shoes to discriminate the activity of running. In a more advanced configuration, proximity to running shoes may be combined with GPS signals, heart rate sensor and/or motion sensor output to allow the activity calculator to determine the type of activity being performed, the duration of the activity, and the intensity of the activity.
When the user uses the system for the first time, he or she may designate certain movement patterns as correlating with certain activities. This will aid to calibrate the activity monitor.
Each of the described activity monitors and sensors is designed to be placed on a single position on the body. Bodily signals such as acceleration and ECG signals, are measured local to the position where the sensor is attached to the object. For example, acceleration measured by an accelerometer on the wrist includes motion of the arm, which is not detected by an accelerometer mounted on the waist.
The existing activity monitors, including for example a wrist strap or a waist belt, are often designed to be worn on one place on the body. The existing activity monitor is calibrated such that it provides accurate results if it is attached at a predefined location on the body. If the activity monitor is attached at a different location, the measured activity may be less accurate. If the activity monitor is not attached at the reference position, errors exceeding 5% in the estimation of energy expenditure may occur. This amounts to an error exceeding approximately 100 kilocalories per day.